Method of forming and maintaining refractory bottoms of open hearth furnaces for the manufacture of steel



July 5. 1

Filed Oct. 2, 1962 R. C. OSWALD ETAL METHOD OF FORMING AND MAINTAINING REFRACTORY BOTTOMS OF OPEN HEARTH FURNACES FOR THE MANUFACTURE OF STEEL 2 Sheets- Sheet INVENTORS.

RAYMOND C. OSWALD, ALBERT L. RENKEY,

DALE R. PFLAUMER &

HARRY GUY BY MAUK ATTORNEYS y 5, 1966 R, c, OSWALD ETAL 3,259,672

METHOD OF FORMING AND MAINTAINING REFRACTORY BOTTOMS OF OPEN HEARTH FURNACES FOR THE MANUFACTURE OF STEEL Filed Oct. 2, 1962 2 Sheets-Sheet 2 INVENTORS.

RAYMOND c. OSWALD. ALBERT L. RENKEY.

DALE R. PFLAUMER & HARRY GUY MAUK 'V/waw, M

ATTORNEYS United States Patent 3,259,672 METHOD OF FORMING AND MAHNTAINING RE- FRACTORY BOTTOMS OF OPEN HEARTH FUR- NACES FOR THE MANUFACTURE OF STEEL Raymond .C. Oswald, Poland, Ohio, Albert L. Renkey, Pittsburgh, Pa., Dale R. Pflaumer, Poland, Ohio, and Harry Guy Mauk, Pittsburgh, Pa., assignors of one-half to Sharon Steel Corporation, Sharon, Pa., a corporation of Pennsylvania, and one-half to Harbisou-Walker Refractories Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 2, 1962, Ser. No. 227,818 6 Claims. (Cl. 264-30) The invention relates to open hearth furnaces, and more particularly to methods of forming, installing and maintaining an integral, cast, uniform, dense, highly refractory bottom or hearth for a furnace such as an open hearth furnace for the manufacture of steel.

It has been standard practice in the steel industry to form open hearth furnace hearths from magnesite refractories having a high magnesia (MgO) content, since magnesia is the best basic refractory known for holding molten metal in steel-making furnaces, and for resisting the high temperatures and chemical attack which occur in the operation of such furnaces.

Many years ago open hearth furnace bottoms or hearths were installed by burning in successive layers of grain magnesite to the desired or required thickness and contour upon a magnesite brick sub-hearth. This mode of hearth installation was costly and time-consuming, and led to the development some years ago of magnesite refractories which could be rammed in place to the proper depth upon a magnesite brick sub-hearth to form open hearth furnace bottoms.

Even though considerable furnace downtime may be saved in the initial installation of a rammed magnesite refractory bottom, as compared with the earlier method of installing a sintered bottom, inherent difficulties are involved in the operation and use of open hearth furnaces having rammed bottoms. In one steel plant over a period of years of operation of many open hearth furnaces, an average of 40 minutes per heat delay has been involved for maintenance of and repairs to the rammed bottoms of the furnaces.

Unfortunately, because of the human factor involved in ramming the granular magnesite refractories in place in forming a rammed bottom, it is impossible from a practical standpoint to obtain uniform density of the rammed bottom material throughout the entire hearth. This lack of uniformity results in stratification, soft spots, holes, etc., which form during furnace steel melting operations and which must be patched or repaired. The resultant average 40 minutes per heat furnace downtime delay for bottom repairs and maintenance including fettling not only is costly and time-consuming in and of itself, but it represents a furnace production time loss which adds to the cost per ton of steel produced.

Furthermore, since some furnace cooling and reheating is necessarily involved when .an open hearth furnace is down for an average of 40 minutes per heat for bottom repairs, furnace roof life may be affected and furnace roof repair and maintenance costs may be increased due to the repeated cooling and heating of the refractory roof components which may cause thermal shock or other damage to the roof components incident to the downtime for bottom repairs.

Accordingly, there has been a long existing need in the art for reducing the time required to install a new open hearth furnace bottom; for eliminating the lack of uniformity inherent in rammed furnace bottoms; and for significantly reducing the maintenance and repair costs 3,259,672 Patented July 5, 1966 and furnace downtime involved for delays for bottom repairs in the operation of open hearth furnaces.

It has been proposed by others to attempt to eliminate the inherent difficulties experienced with rammed open hearth furnace bottoms by casting an entire open hearth bottom, employing high-magnesia ramming compositions which had been used previously in rammed bottom installations, and consolidating the ramming material by the use of concrete vibrators to eliminate entrapped air and to achieve good compaction of the granular refractory material. However, an attempt to cast an entire open hearth bottom in this manner from refractory ramming compositions resulted in failure due to explosion of the bottom material during heating thereof to dry out the cast bottom and to develop the necessary ceramic bond; and prior to the present invention the need in the art continued to exist.

Accordingly, it is a general object of the present invention to provide a new method of and procedure for installing an integral, cast, uniform, dense, highly refractory bottom in an open hearth furnace which substantially reduces the time heretofore required for installing or replacing open hearth furnace bottoms.

Furthermore, it is an object of the present invention to provide a new method of and procedure for installing an integral, highly refractory bottom in an open hearth furnace which eliminates the lack of uniformity heretofore inherently characterizing rammed furnace bottoms, and which produces an integral, cast, bottom structure of the magnesite hearth material containing over magnesia (MgO), that is at least 90% MgO by weight on the basis of an oxide analysis, having a density equivalent to that of conventionally rammed materials, with extreme uniformity of the high density characteristic throughout the cast bottom structure.

Moreover, it is an object of the present invention to provide a new method of and procedure for installing a refractory bottom in an open hearth furnace containing over 90% magnesia (MgO) which produces an integral, cast bottom structure that requires approximately an average of only three to six minutes per heat furnace downtime delay for bottom maintenance and repairs over periods of hundreds of heats of furnace operation in the manufacture of steel of a wide carbon content range of from .03% to .79% carbon, as compared with prior.

rammed bottoms which have required an average of forty minutes delay per heat furnace downtime for bottom maintenance and repairs.

In addition, it is an object of the present invention to provide a new method of and procedure for installing a refractory bottom containing in excess of 90% magnesia (MgO) in an open hearth furnace which produces an integral, cast bottom structure characterized by substantially reduced maintenance and repair costs and furnace downtime in furnace operation.

Also, it is an object of the present invention to provide a new method of installing a refractory bottom in an open hearth furnace which produces a bottom structure having a longer life and requiring less fettling than prior bottom structures as a result of the uniform high density refractory structure developed which substantially eliminates the occurrence of stratification, soft spots, etc.

In addition, it is an object of the present invention to provide a new method of and procedure for installing an integral, cast, uniform, dense, highly refractory bottom in an open hearth furnace which avoids or eliminates furnace bottom difiiculties and problems which heretofore have been encountered in the operation of open hearth furnaces.

Further, it is an object of the present invention to provide a new method of maintaining a refractory open hearth furnace bottom structure formed or installed in accordance with the invention, such that the bottom structure has a longer life, requires less fettling, retains a higher magnesia (MgO) content for longer periods of furnace operation, and retards the rate of depletion of the magnesia (MgO) content of the furnace bottom in use.

Finally, it is an object of the present invention to prc vide a new method of and procedure for installing a refractory open hearth furnace bottom structure which can be used readily and conveniently, to replace the bottoms in existing open hearth furnaces for solving the stated problems in the art and eliminating the difliculties enumerated, and to obtain the foregoing advantages and desiderata in a simple and effective manner.

These and other objects and advantages apparent to those skilled in the art from the following description and claims, may be obtained, the stated results achieved, and the described difiiculties overcome by the methods, steps, operations, procedures, and new uses of known processes, compositions of matter or materials, which comprise the present invention, the nature of which is set forth in the following general statements, preferred procedures of whichiilustrative of the best modes in which applicants have contemplated applying the principles-are set forth in the following description and shown in the drawings, and which are particularly and distinctly pointed out and set forth in the appended claims forming part hereof.

The problem with which the art has been plagued may be solved and the existing need in the art satisfied by our discoveries of a new process for installing a highly refractory bottom for an open hearth furnace by which a uni form, dense bottom having a magnesia (MgO) content in excess of 90% may be successfully cast. Associated with these discoveries and following the successful casting of an integral, cast, uniform, dense, highly refractory open hearth furnace bottom are the further discoveries that such furnace in operation and use for melting and refining steel in a wide carbon content range has characteristics heretofore unknown in the open hearth furnace art, particularly when bottom maintenance is carried out in accordance with further discoveries of the invention.

In accordance with the invention and these discoveries, the sub-hearth brickworkof an open hearth-furnace is entirely exposed and the surfaces thereof treated to prevent absorption of Water from the castable material. Preferably forms then are installed contoured to the profile of the sub-hearth surfaces and to the profile desired for the resultant cast bottom dividing the sub-hearth into sections defining cavities extending generally from front to back of the hearth.

A magnesite refractory material which may be used for forming the bottom in accordance with the invention is the commercial product of Harbison-Walker Refractories Company, of Pittsburgh, Pennsylvania, known by the trade name H-W =Perimix. H-W Perimix is an extremely refractory dead-burned magnesite castable mate, rial of high purity periclase, having a magnesia content of about 90% and is available in dry condition. After mix ing with a carefully controlled amount of water for use, it sets very rapidly, develops high strength upon drying and has excellent stability of volume even at very high temperature. H-W Perimix is a size-graded dry castable mix. The screen sizing (Tyler screen sizes and by weight) typically is:

%4 on 10 mesh %1O on 28 mesh 35%minus 65 mesh The dry magnesite castable material is mixed by careful control with preferably 8% by Weight of water, care being taken to obtain a thorough and uniform The careful control of the amount of water added in the mix is important from many standpoints. Since a typical open hearth furnace bottom may require as much as 120 tons of magnesite refractory material, over 9 tons of water will be mixed with the castable material which must be evaporated from the cast bottom during the drying-out and burning-in period. The disposal of such a large amount of water vapor coming from the water mixed is a difficult operation. Thus, it is important not to have more water mixed with the dry castable refractory material than is required for the successful casting of the refractory material.

On the other hand, it is equally necessary to have sufficient water added to the dry castable refractory material for completing the necessary reactions to achieve an hydraulic bond or set. Furthermore, it is important to have sufficient water in the mix so that the wet refractory material mix can be conveyed from a mixing station With all possible speed but without special handling precautions to the immediate hearth area where the wet mix is being cast. An excess of water, however, must be avoided from this standpoint, because it can cause conveying problems, loss of material, etc; The expression wet refractory material mix denotes a workable plastic material amenable to flow under vibration.

Furthermore, sufficient water must be present in the mix so that vibration thereof can be performed efiiciently to rapidly develop the highest possible density, compaction and random orientation of the particles of the refractory material. At the same time, excess water during and following compaction must be guarded against, since an accumulation of any substantial body of water on top of the compacted material must be avoided to prevent spallin'g of the material during the dry-out period in the zones where any abnormal concentration of water may occur.

Weather has a decided affect upon the moisture requirement of the mix. In hot dry weather (above about F.) working with a hot furnace the amount of water should be increased as otherwise it may be evolved too fast for proper setting conditions. The contrary is true in cold weather or under more humid conditions or Working with a cold furnace. Accordingly, as indicated, the preferred amount of water to be mixed with the dry castable refractory material may be 8% by Weight, although the careful control can be achieved if the water content falls within the narrow range of 5%10% by weight of Water.

The castable refractory material mixed with the controlled amount of water is then delivered in as large a volume and as rapidly as possible by driven conveyers directly to the immediate area to be cast. It is shoveled in place as rapidly as possible to the required depth in a cavity provided by the forms. Vibration of the deposited wet refractory material then is carried out for developing the desired density as rapidly as possible; and this may be accomplished using typical immersion concrete vibrators.

Here again, it is important to accomplish the steps of mixing, conveying, depositing and vibrating the refractory material in the shortest time interval possible for any given volume or weight of material because the preferred castable refractory material is a quick-setting material and only a short time interval is available after mixing with Water within which the casting operations must be completed in order that uniformity throughout the entire cast can be obtained.

The center cavity section of the furnace bottom fiat with which the tap hole connects is cast first so that the proper slopes can be established for the contour of the cast bottom from front to back and from center to ends of the hearth flat. After the casting of the center section is completed, alternate sections provided by the forms, spaced from the center section preferably are cast next. The casting of the alternate sections at either side of the center section preferably is carried out at the same time. In this manner it is possible to strip the forms from the center section while work is proceeding with thecasting of the alternate sections. After the alternate sections have been cast and the material set, the forms are stripped therefrom and intervening sections between the alternate sections and the center sections are cast, using the cast sections as forms for the casting of material in the intervening sections and also using the completed center and alternate sections as grades for forming the desired slope throughout the furnace fiat. In this manner, an excellent bond is obtained between the edges of the refractory material masses cast in the intervening sections and the edges of the previously cast material used as forms; and also the desired slopes may be formed most accurately.

Front, rear and end wall bank sections of the bottom then are cast in a similar manner, section by section, using step forms or flat forms extending up the bank walls to the desired contour.

The forms are stripped from the last cast sections as soon as the cast material therein has set sufliciently. Combustion burners are inserted into the furnace and lighted to heat the cast material as rapidly as possible to dry out the cast material. This drying out should be accomplished as rapidly as possible, preferably by maintaining an increase of at least 75 F. per hour until a temperature of 2900 F. is reached. During the first part of the drying-out operation or until the temperature reaches about 800 B, it is difficult to maintain the 75 F. per hour heating schedule because of the difiiculty of maintaining burner combustion within the furnace chamber and at the same time of disposing of the large amount of water vapor in the system coming from the water mixed with the refractory material cast. The furnace should be vented to the maximum degree possible for removing the water vapor formed and for preventing condensation during the heating-up period at the ports around the burners, at the doors and at other cool zones in the furnace, so as to prevent dripping of condensed water onto the cast material being heated for the removal of water as fast as possible.

After the cast bottom has been heated to a temperature of about 2900 F., the heating is continued for 2.4 hours, maintaining a 2900-3000 F. temperature, to develop ceramic bonds in the refractory material and to complete for formation of the integral, cast, uniform, dense, highly refractory bottom.

After the cast bottom has been installed the usual open hearth steel melting and refining procedures may be carried out in the furnace; and in accordance with the invention the cast bottom structure is maintained between heats by fettling with high-purity magnesite having high magnesia (MgO) content such as sea water magnesite.

By way of example, the new process or procedure for installing highly refractory open hearth furnace bottoms is shown diagrammatically in the accompanying drawings forming part hereof, wherein:

FIG. 1 is a diagrammatic view illustrating equipment use for practicing the invention;

FIG. 2 is a diagrammatic plan sectional view illustrating the manner in which forms may be installed to divide the furnace hearth into sections for casting a refractory-bottom and indicating the general location of the wet mix distributing conveyers by dot-dash lines;

FIG. 3 is a diagrammatic sectional view looking in the direction of the arrows 3-3, FIG. 2;

FIG. 4 is a diagrammatic sectional view looking in the direction of the arrows 4-4, FIG. 2;

FIG. 5 is a diagrammatic sectional view similar to FIG. 4, illustrating a later stage in the installation procedure after the furnace flat has been cast and showing step forms for casting the bottom bank wall areas; and

FIG. 6 is a view similar to FIG. 5 showing a modified arrangement of forms for casting the bottom bank wall areas.

Similar numerals refer to similar parts throughout the various figures of the drawings.

Although the invention is illustrated and described specifically and in detail with relation to the installation of a bottom for an open hearth furnace, it is not the intention to limit the invention to bottoms or hearths for open hearth furnaces since the discoveries and principles of the invention may be used in forming the bottoms or hearths of other melting furnaces or molten metal containers, such as basic oxygen furnaces, L-D converters, Kaldo converters, etc., any of which must contain or hold high temperature molten metal and must resist both the high temperatures and chemical attack which may occur in the use of such equipment.

The use of the process, principles, procedures and discoveries of the present invention to produce the first known successful installation of an integral, cast, uniform, dense, refractory bottom containing in excess of (MgO) magnesia for an open hearth furnace involved a furnace having approximately a 12 /2 x 40 foot flat area of exposed sub-hearth brickwork and required some tons of dry castable refractory material to form the integral bottom having approximately a 17-inch average thickness for the flat and bank wall areas.

Although the invention is described herein in detail with respect to this particular furnace, it is to be understood that the same principles, procedures and discoveries can be used in installing bottoms in larger open hearth furnaces where say 200-300 tons of refractory bottom material may be required to be cast to form an integral bottom.

Equipment used for practicing the invention includes a high capacity mixer 1 capable of handling the dry castable refractory material to be mixed and cast in batches say of 1500 pounds or more at a time for rapidly, thoroughly and uniformly mixing 8% by weight of water with the dry refractory material. The mixed material is discharged from the mixer 1 onto a bridging or mix conveyer 2 extending through one of the access or charging openings 3 in the front wall 4 of the furnace 5. Mix conveyer 2 discharges within the chamber 6 of the furnace 5 preferably into a hopper 7 supported therein. Hopper 7 has a discharge opening 8 located above a placing conveyer 9 movably supported within the chamber 6 so that the Wet refractory mix may be discharged or deposited therefrom onto the sub-hearth brickwork 10 of the furnace 5 as close as possible to the immediate vibration area where the material will be shoveled in place.

The placing conveyor 9 is movable within the furnace chamber so that the wet mix may be discharged as close as possible to the vibration area. Both the mix conveyer 2 and the placing conveyer 9 are positively driven conveyers either of the shaker or belt type, so that the mixed maferial can be deposited at the vibration area as quickly as possible after mixing.

Although only one mixer 1 is illustrated diagrammatically in the drawings, a plurality of mixers may be used, depending upon the size of the hearth to be installed. Each mixer 1 will be served by a mix conveyer 2 and a placing conveyer 9 in order that the wet mix may be supplied to the hearth areas being cast at the rate of some 8 to 20 net tons per hour.

The dry refractory material is received from the supplier either in bags or polyethelene lined containers, the latter of which may hold a large amount such as 1500 pounds of material. The dry material is delivered or charged to the mixer 1 from the shipping containers for the material by power skips, a payloader bucket or a scoop attachment on a fork-lift truck. The water added to each batch of dry refractory material to be mixed is preferably delivered to the mixer 1 in the controlled amount required through a hose 11 having a stop cock valve 12 and a water meter 13 so that precise measurement and speedy discharge to the mixer can be obtained.

In this manner the water and dry refractory material can be mixed in a little over a minute and, meanwhile, the payloader can be reloaded with a new charge of dry material. The wet mix can be discharged from the mixer 1 onto mix conveyer 2 in about 2 minutes. The wet mix is then delivered rapidly by the driven conveyers to the vibration area where it is shoveled in place.

In successfully casting the bottom in the described 12 /2 x 40 foot fiat hearth area, H-W Perimix was used as the dry castable refractory material and the flat was laid in five sections as illustrated in FIGS. 2, 3 and 4. Forms 14, 15, 16 and 17 were provided, contoured to the profile of the sub-hearth brickwork 10. A inch per foot slope was to be maintained in the finished bottom from the front wall 4 to the back wall 18 of the furnace, and a /2 inch per foot slope was to be maintained in the finished bottom from the tap hole zone 19 at the center of the furnace near the back wall to the end or bridge walls 20 and 21. These forms were secured by braces 22a angled down from the front and back walls. The center forms and 16 were braced by stringers 22 to the end forms 14 and 17; and the end forms 14 and 17 were braced by stringers 23 to the bridge walls and 21. Thus, the forms 14, 15, 16 and 17 defined five cavities 24, 25, 26, 27 and 28 extending on the fiat from front to back of the hearth. The center cavity or section 26 was clear of braces and cast first, the wet mix being delivered thereto preferably working from back to front.

In delivering the wet mix to the center section 26, the hopper 7 and placing conveyer 9 were temporarily moved away from the discharge end of mix conveyer 2 so that mix conveyer 2 delivered the wet mix directly to the center section 26. Mix conveyer 2 was supported so that it could be moved endwise to locate its discharge end within the furnace immediately above the center section area onto which the wet mix was to be deposited.

After being shoveled in place, the wet mix was immediately vibrated with immersion vibrators to compact the material and develop the maximum density. Some 25,500 pounds of material (17 mixes of 1500 pounds each of dry refractory material and 8% water) were required to fill the center section cavity 26. The material was mixed and deposited at the vibration areas, and the progressive vibration thereof as deposited was completed in approximately 1 /2 hours.

Bridge wall braces 23 were then removed and thetwo end sections 24 and 28 were cast involving the deposit of some 63,000 pounds of dry refractory material plus the required amount of water supplied by 42 mixes and was accomplished in approximately 3 hours. In this instance, the cavity 28 was cast first followed by casting cavity 24 since only one mixer 1 was used with one set of mix and placing conveyers. Before the wet mix was delivered to the cavities 28' and 24, the hopper 7, indicated in dot-dash lines in FIG. 2, was relocated beneath the discharge end of mix conveyer 2; and placing conveyer 9 was adjusted to position it to receive material from hopper 7 and to discharge such material at the immediate area in either cavity 28 or 24 where placement and vibration of the wet mix occurred. Again, because the mix conveyer 2 could be moved endwise, because hopper 7 could be moved to a location beneath the delivery end of mix conveyer 2, and because mix conveyer 9 could be swung and also moved endwise, the delivery of wet mix to the particular area being vibrated in cavities 28 and 24 was accomplished with great rapidity.

Had two mixers and separate sets of conveyers served thereby been used, both cavities 24 and 28 would have beencast at the same time to reduce the elapsed time required for casting the wet mix in the two sections. Within /2 hour after the cavity 28 was cast, forms 16, 17 and 22 were pulled and cavity 27 was cast immediately with 28,500 pounds of material provided by 19 mixes in about 1 /2 hours. Thereafter, forms 14, 15 and 22 for cavity were pulled and that cavity was cast within about 1 /2 hours with 27,000 pounds of mate-rial provided by 18 mixes.

Forms 14, 15, 16 and 17 were provided with wooden strips 29 which gave a dove-tailed effect to the case joints between the material cast in cavities 25 and 27 and in adjacent cavities 24, 26 and 28. An excellent bond was 8 obtained at the cast joints between the material cast in cavities 24, 25, 26, 27 and 28.

Prior to the deposit and casting of any of the wet mix, all sub-hearth brickwork surfaces were given a coating of sodium silicate to prevent the absorption of moisture from the mix by the sub-hearth brickwork.

Forms then were provided (FIG. 5) along the bank and end walls so that refractory material could be cast in climbing zones in a series of steps 30 along the front, back and end walls. Casting of the steps was started as soon as forms were placed at one end. Material was cast simultaneously from the end on both front and back steps progressing toward the other end. As one step was completed at one end, forms were ready at the opposite end to start with the next step. Upon completion of the last step, material was feathered up the walls by hand. In casting the steps 30, the material was progressively vibrated as deposited to develop the uniform maximum density.

In the installation described, 72 tons of H-W Perimix was used for casting the flat, and 47.5 tons for the steps, totaling 119.5 tons of H-W Perimix for the complete bottom supplied by 159 sepaarte mixes of 1500 pounds each. The total elapsed time was 18 hours and the actual working time was 16 hours and 25 minutes. Thus, on the average, the material from each mix was mixed with water, conveyed to the vibration area and vibration thereof completed within 6.2 minutes average. This average time interval was sufiicient to enable casting and vibration of the wet mix to maximum density before the material set. Substantially immediately after vibration of the material in any area was completed, the material had set or was in a physical state such that workmen operating the immersion vibrators in adjacent areas could walk on the material that had been cast.

The total 16.5 hours working time for pouring the bottom illustrated, can be reduced substantially by using two mixers and two sets of conveyers serving the mixers, so that the casting of cavities 24 and 28 and 25 and 27 can proceed simultaneously as well as the pouring of the climbing or bank areas. In any event, the material would be mixed, deposited and vibration completed within 5 to 15 minutes and preferably within 5 to 10 minutes for casting any particular batch of the wet mix.

Although the forms have been illustrated as being constructed of wood, adjustable metal forms can be used. Also prefabricated forms with flat containing members 31 can be used in the climbing areas on the walls as illustrated in FIG. 6 instead of the step forms 30a illustrated in FIG. 5. The only requirement is that the material be contained in the climbing areas as indicated at 32 while being immersion vibrated to develop maximum uniform density prior to setting.

As soon as the cast material in the climbing wall areas had set, the step forms 30a were removed and combustion burners were introduced into the furnace and lighted to dry out the cast refractory material. Although a heating schedule of at least F. per hour increase in temperature was desired which is a normal or typical heating schedule for forming in magnesite refractory material after it has dried out, it was impossible to maintain this heating schedule until the temperature reached approximately 800 F. because of difiiculties in maintaining burner combustion due to the large amount of water vapor in the system coming from the over 9 tons of water in the material. During the dry out, it is important to maintain adequate ventilation so as to dispose of the water vapor as rapidly as possible.

After a temperature of about 800 F. was reached, the heating schedule continued substantially in accordance with the typical 75 F. per hour increase in temperature until a temperature of 2900 F. to 2950 F. was reached. Thereafter, the temperature was maintained at between 2900 F. and 3000 F. for a 24 hour sintering period to develop the desired ceramic bonds in the cast refractory furnace bottom material.

Inspection of the vibration-cast hearth after development of the desired ceramic bonds by siutering disclosed no evidence of any separation or joints between the five sections of the hearth sequentially deposited and vibrated in the cavities 24, 25, 26, 27 and 28. Bonding was achieved in a vertical plane between the sections, so that an integral, monolithic, uniform, high density, ceramically bonded, refractory bottom structure resulted.

At the conclusion of the sintering period the surfaces of the cast bottom were dusted with Cape May magnesite, a high-purity sea water magnesite on the step areas, and a light dressing of H-W Perimix was applied to the flats. The tap hole was cleaned out and filled with dead burned dolomite. The furnace was then charged in accordance with usual practice with scrap, lime, heavy scrap and pig iron and a steel heat was produced.

The furnace with a refractory bottom cast as described and in accordance with the invention was in continuous production for 272 heats, producing 42,406 tons of steel,

averaging 155.9 net tons per heat, with an average of 6 hours and 56 minutes heat time tap-to-tap over the entire 272 heat period of operation. A total of only 895 minutes was required for repairs to and fettling of the bottom and 100 minutes was the total time for tap hole delays. This amounts to a 3.29 minutes average bottom and banks delay per heat, and 0.37 minute average top hole delay per heat, totaling 3.66 minutes average delay for bottom, banks and tap hole, fettling and maintenance.

This record of bottom maintenance delay of 3.66 minutes per heat may be compared with the average experience in the operation of open hearth furnaces with rammed bottoms of 40 minutes delay per heat for bottom repairs and maintenance.

This substantial reduction in time for bottom maintenance aided in increased furnace production. Thus, the furnace in a 31-day month produced 16,280 net tons of steel, as compared with the previousrecord for the same furnace with a rammed bottom of 15,035 net tons of steel.

Furthermore, the furnace was operated for the 272 heats without cleaning the slag pockets and flues as compared with an average of about 200 heats which previously have been made between shut-downs for cleaning out slag pockets and flues. Such a slag and flue cleaning operation normally requires three to four days furnace downtime.

After the continuous furnace operation for 272 heats it became apparent that slag pockets and fiues would have to be cleaned shortly. However, the furnace was operated for eight more beats and after a total of 280 heats of continuous furnace operation, the furnace was shut down for clean-out and repairs. During the last eight heats, bottom, banks and tap hole, fettling and maintenance on the average required a little more time per heat so that the total average delay per heat for the entire 280 heats was 3.82 minutes per heat as compared with the 3.66 minutes per heat average over the first 272 heats.

Of course, the type of steel made during the 280 heat operation varied somewhat from heat to heat. However, low carbon steel was made during such 280 heat operation averaging a little over .10% carbon steel in the range from 0.03% to .24% carbon steel.

After the flue clean-out and repairs had been accomplished, the furnace was again placed in operation and 234 additional heats of steel were made therein. In the 234 heat operation, higher carbon steels sometimes were made within the range of .03% to .79% carbon. The production of higher carbon steel involves the use of more lime. This in turn results in lime deposits on the furnace bottom and banks after the heat is tapped. These deposits should be cleaned out after each heat and such cleaning-out was done where high carbon heats were made which involved a loss of time between such beats for draining.

The average delay time per heat where high carbon steel beats are made may be about 9 to 10 minutes per heat including the time consumed for lime deposit clean-out and drainage involved in the higher carbon heat operation. However, the entire 9 to 10 minutes per heat average delay is not attributable entirely to bottom maintenance and repair but must be considered to be made up of an average of about 4 to 6 minutes delay time per heat for bottom maintenance and repair and 4 to 5 minutes per heat for lime deposit drainage, etc. since the latter is a condition separate from bottom maintenance and repalrs.

The average carbon content for the entire 514 heats was a little over .13% carbon and in the range of from .03% to .79% carbon. The total average delay per heat throughout the entire 514 heats including both bottom,

' banks and tap hole maintenance and repairs, and lime deposit drainage time where higher carbon heats were involved, is 6.54 minutes per heat. During the entire 514 heat operation 81,331 net tons of steel ingots were produced averaging 158.2 net tons per heat and an average of 7.8 hours heat time, tap-to-tap.

The 6.54 minutes average bottom, bank and tap hole delay per heat throughout the 514 heat campaign involved a 5.77 minutes average bottom and bank delay per heat and .77 minute average tap hole delay per heat, and the delays for lime deposit drainage where high carbon heats were involved are included in these figures.

The 6.54 minutes average total bottom, bank and tap hole time delay per heat as compared with the 40 minutes per heat time delay experienced in the past represents a time saving of 33.46 minutes per heat or 17,198.44 min utes over the 514 heat campaign which amounts to 286.64 furnace hours saved. During the 514 heat campaign 20.19 net tons of steel per hour tap-to-tap were produced. Thus, the 286.64 hours saved due to reduced bottom delays represents in effect a furnace production gain of 5,787.26 tons of steel, directly attributable to the reduced bottom delays during the 514 heat campaign.

For many years it was standard practice in fettling the bottom of open hearth furnaces to use raw dolomite, a relatively cheap material, for dressing the bottom after each heat and for replenishing the magnesia content of the bottom material. More recently this practice was changed in the operation of the particular furnace described above, but prior to the installation of the new bottom in accordance with the invention, by using dead burned dolomite as a fettling material. Dead burned dolomite is higher in MgO content but is'more expensive.

Nevertheless, the increased cost appeared justified because of the reduction in the amount of fettling material used to an average of 60-65 pounds of dead burned dolomite per ton of steel ingots produced, and by less furnace downtime for bottom repairs.

After installation of the cast bottom in accordance with the invention and during the operation of the furnace for the 514 heats described, sea water magnesite containing at least about 92% MgO was used as a fettling material in place of dead burned dolomite. Although sea water magnesite costs considerably more than dead burned dolomite, it was discovered that only 14.8 pounds of sea water magnesite per ton of steel ingots produced was required for fettling the new bottom structure over the indicated 514 heat operation of the furnace.

The casting of the refractory bottom in the furnace in accordance with the invention, as described and indicated, was accomplished in 16 hours and 25 minutes as compared with prior three to four day installation time requirements for a rammed bottom. This substantial reduction in the installation time as well as the phenomenal 83.65 %-90.85 reduction in delay time for bottom, tap hole and fettling maintenance, the susbtantial reduction in the amount of fettling material used per ton of steel ingots produced, the increased production of steel by the furnace achieved, and the increased number of heats made before slag pockets and flues were required to be cleaned, all contribute to a decreased cost per ton of steel produced 1 1 in the furnace and to increased utilization of existing facilities.

At no time during the 514 heat operation of the furnace was there any occurrence of soft spots or Stratification of the character and extent which have been typical in the use of rammed bottom furnaces.

Important aspects of the invention are the discoveries of the ability to vibration-cast a castable refractory material as a substantially continuous procedure and to extend the refractory material mass throughout such continuous vibration-casting along an entire open hearth furnace bottom to form an integral, monolithic, highly refractory bottom in the open hearth furnace. In order to extend the continuously vibration-cast mass, the castable refractory material must be a very quick setting refractory composition and only a short time interval is available after mixing with water within which the material can be worked before it starts to set. H-W Perimix is such a material and has excellent room temperature workability which is apparently one of the contributing factors that permits maximum density to be developed rapidly by prompt vibration after placement, despite the quick setting characteristic.

In accordance with the invention, and by rapid handling, delivery and compacting of the refractory material, a wet mix of a castable refractory material with the described controlled amount of water can be delivered, placed and vibrated within the S to minute time interval, and a resultant density of 165-175 pounds and greater per cubic foot compaction developed in and throughout the cast mass, a density equivalent to that of conventionally rammed products.

More important, however, is the further discovery that in proceeding to place and to vibrate as placed, the indicated wet mix of a castable refractory material such as H-W Perimix, the resultant density of the integral bottom formed is substantially uniform throughout, including monolithic bonding of the material between successive sections cast, even though the material is delivered, placed and vibrated from successive batch mixes, and cast in successive sections. The delivery and vibration of the material, even though mixed in batches, is in effect a continuous procedure, because of the use of the driven conveyors, and the use of movable conveyors within the furnace chamber so that the material delivered can be deposited right at the vibration area.

In other words, the new procedure involves the placing and the immediate vibrating as placed, of a large mass of quick-setting castable refractory material and the extending of the placement and vibration compactment to conform to planned contours of a furnace hearth, so as to develop uniform density and particle orientation throughout the entire cast area even though the wet mix of castable refractory material is delivered successively to different portions of the entire area.

The vibration-casting of large masses of castable refractory material in accordance with the principles of the invention differs fundamentally from known procedures for vibration-casting large bodies of concrete. In the latter instance, the concrete mix as poured is soupy and fluid. Where large concrete masses are involved having a shallow depth extending over a large area, a section of the same confined by forms is filled with the soupy mix and the entire soupy mix body is vibrated to achieve cavity fill-in, to release entrapped air, and to speed up the chemical reactions which occur.

On the other hand, in the vibration-casting of the relatively shallow depths and large area of a large mass of castable refractory material in accordance with the invention, the wet refractory mix is neither soupy nor fluid, and the vibration and setting of the material proceeds rapidly, progressively and continuously as the material is deposited or placed from one zone to another within any particular area.

The uniform, extremely dense and highly refractory characteristics of the resultant monolithic integrally cast bottom after burning in and during use are demonstrated by the 83.65% to 99.85% reduction in time for bottom maintenance delays, and by the substantial reduction in the amount of fettling material per ton of steel ingots produced, etc., discovered as characterizing the resultant bottom after a 514 heat campaign of furnace operation.

it long has been known that the magnesia content of open hearth furnace bottoms in effect becomes depleted in use because of absorption of slag components, iron, etc. In some cases in the past the magnesia content of the bottom has been reduced to as low as 20% by weight. The usual fettling of bottoms after each heat restores some of the depleted magnesia content.

It is believed that the high density and density uniformity of the resultant integrally vibration-cast bottom, together with the high-purity periclase component of the castable refractory material used produce a cast bottom structure which resists the tendency of absorption of slag and iron or reduces the rate at which these materials are absorbed. This is demonstrated by the substantially reduced amount of fettling material used per ton of steel ingots produced, and by the 83.65%90.85% reduction in time for bottom maintenance delays achieved in the 514 heat campaign of a furnace having a refractory bottom installed and maintained in accordance with the principles and discoveries of the invention, as compared with maintenance required by and fettling requirements of prior rammed bottom structures.

Furthermore, the use of sea water magnesite containing at least about 92% MgO as a fettling material for the uniform high density inte ral vibration-cast refractory bottom structure initially composed of about MgO achieves the important combined result of reducing the amount of fettling material required per ton of steel ingots produced and apparently of maintaining a higher magnesia (MgO) content in the bottom structure during use for longer periods of time.

While a complete explanation of how this phenomena occurs may not be fully understood, it is believed that the high-purity and uniformity of the Mg() content of the cast bottom structure retards the rate of depletion of the MgO content thereof and that since the sea water magnesite fettling material contains at least about 92% MgO, restoration of some of the depleted MgO content of the bottom structure occurs from the fettling operation without any appreciable amount of any impurity or component derived from the fettling material being absorbed in the bottom structure.

That is to say, MgO and substantially nothing else is added when fettling, so that sea water magnesite acts most efficiently with minimum required amounts to restore some of the MgO content of the hearth structure.

Another important aspect of the present invention is the ability to dry out and burn in a vibration-cast hearth formed from a castable refractory material having a size graded m xture of refractory having high MgO content and to accomplish the drying out rapidly, contrary to past attempts to vibration-cast an entire open hearth furnace using commercial ramming refractory materials which exploded during drying out and burning in.

The exact explanation of the mechanisms involved are not known. However, it seems that when it is attempted to dry out an entire hearth vibration-cast using commercial ramming mixes, an amorphous hydrated complex develops, the physical condition of which is such that it forms impermeable occlusions in the mass. When the complex gives up both free and combined water, because of its impermeability, steam builds up within the mass and explodes.

On the other hand, the texture and physical character of the green bonding complex formed in an open hearth furnace bottom vibration-cast from I-I-W' Perimix type refractory material is such that upon heating up the cast structure, the free and combined water is readily released from the mass and no steam is built up or retained within 13 the mass to explode. Thus, the mass can be heated up at the fastest possible rate consistent with removal of the released water vapor from the furnace chamber with the rapidity necessary so that combustion can be maintained at the burners supplying the heat for the drying out operation.

' Accordingly, the present invention provides a new method of and procedure for installing an integral, vibration-cast, uniform, dense, highly refractory bottom in an open hearth furnace which substantially reduces the time heretofore required for such installation; provides a resultant vibration-cast hearth characterized 'by an 83.65% to 90.85% reduction in time for bottom maintenance delays, and a substantial reduction in the amount of fettling material used per ton of steel ingots produced, as compared with past bottom maintenance and fettling experience; provides a resultant bottom with which increased steel production can be achieved, and an increased number of heats made before slag pocket and flue cleaning is required; and provides for the production of steel at a decreased cost per ton of steel produced.

Thus, the improvements and discoveries of the invention provide the described advantages, overcome prior art difficulties that have been troublesome and costly, enable increased utilization of existing facilities, and solve existing problems in the art.

In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are utilized for descriptive purposes herein and not for the purpose of limitation and are intended to be broadly construed.

Moreover, the description of the improvements is by way of example, and the scope of the present invention is not limited to the exact details illustrated or the exact dimensions described. For instance, although for the particular furnace in connection with which the installation of a vibration-cast hearth has been described, it was indicated that a 17-inch average bottom thickness was provided, this bottom thickness can be varied to suit the particular requirements of the particular furnace having a vibration-cast bottom installed therein. Further, although H-W 'Perimix was used in accordance with the discoveries, other castable refractory materials having properties comparable to H-W Perimix would be suitable provided such castable refractory materials are fast setting, are characterized by case of evolution of free and chemically combined water, and the refractory grain is in a highpurity dead burned state. The castable refractory material also should be capable of rapidly becoming self-sustaining to a degree sufficient to support the weight of workers without permanent deformation.

In the fcergoing, the invention has been described utilizing rigid forms to predetermine and predefine zones to be sequentially cast in the furnace bottom. This is a preferred arrangement. Other arrangements also are possible. For example, when using a casting material having the qualities discussed above and capable of more rapidly forming a self-sustaining mass without losing its amenability to flow under vibration, extensive form construction may not be necessary. In such an instance, for example, a plurality of relatively thin strips, rods, or the like may be inserted between the brick of the open hearth subhearth over substantially the entire area to be cast. The rods are of such length as to predefine the depth to which the material is to be cast on the various zones of the subhearth including the fiat, banks, taphole, etc. With this arrangement, the premixed castaible is continuously and rapidly conveyed and deposited at predetermined zones on the subhearth, where it tends to rest in relatively self-sustaining masses or deposits. Vibrating mechanism is then rapidly applied to these deposits, and they are caused to flow and unite with adjacent deposits. The united deposits are capable of sustaining the weight of workers without permanent deformation. The deposition and vibration is continued until the level of the vibrated material is uniformly even with the extremities of the rods extending upward from the brickwork. The rods are then removed and vibration continued until the holes formed by the rods are eliminated. The foregoing results in a uniform, integral, dense, monolithic bottom.

Having now. described the features, discoveries and principles of the in ention, the procedures of preferred method steps thereof, and the actual successful installation, extended use :and maintenance of an open hearth furnace bottom in accordance with the invention, and the advantageous, new and useful results obtained thereby; the new and useful methods, steps, operations, procedures, discoveries, principles and new uses of known processes, compositions of matter or materials, and mechanical equivalents obvious to those skilled in the art, are set forth in the appended claims.

We claim:

1. The method of forming from a large mass of 119.5 and more tons of refractory material an entire cast, jointfree, monolithic, uniformly and extremely dense, highly refractory furnace bottom on hat and sloping front, back, end and bank sub-hearth brickwork walls of an open hearth furnace including the steps of applying treatment material to the surface of the sub hearth brickwork walls to prevent the absorption of water from subsequently applied c-astable material; providing form tmeans contoured to the profile of the sub-hearth flat and sloping front, back, end and bank walls dividing the sub-hearth flat into cavities each extending from the front to the back bank wall and into climbing cavities extending along the sloping bank walls; rapidly batch-mixing 5% to 10% by weight of water with dry castable refractory material, said refractory material being made from dead burned magnesite having an MgO content of at least about by weight on the basis of an oxide analysis and said castable refractory material being characterized by being quick-setting upon being cast further characterized by a green bonding complex which readily releases free and combined water upon being heated after casting and setting; rapidly substantially continuously conveying immediately after mixing successive batch-mixes of the refractory material to and deposit-placing the same in successive adjacent zones of said cavities; extending the placement of the mixed material from zone to zone throughout each cavity and in successive cavities along the flat and bank walls; progressively vibrating the refractory material in each Zone simultaneously with deposit continuously from zone to zone throughout all said cavities to compact and develop high density in the thus-cast refractory material and to eliminate joints between said zones, meanwhile removing the form means defining any cavity :after the refractory material has been compacted in such cavity; completing the mixing, conveying, deposit-placing and compacting of the thus-cast refractory material of any batch-mix within 5 to 15 minutes; permitting the thus-cast refractory material to set; then combustion heating the cast bottom material to about 800 F. as rapidly as possible to remove water therefrom while simultaneously venting and 'discharging from the furnace chamber water vapor resulting from such water removal during such heating; then rapidly combustion heating the cast material to 2900 F. to 2950 F.; and then continuing the combustion heating of the cast material at between 2900 F. and 3000 F. for 24 hours to develop ceramic bonds in the refractory material and to complete the formation of a cast, joint-free, monolithic, uniformly and extremely dense, highly ref-ractory entire bottom for the open hearth furnace.

2. In a method of forming from a large mass of 119.5 and more tons of refractory material an entire cast, jointfree, monolithic, uniformily and extremely dense, highly refractory furnace bottom on flat and bank sub-hearth brickwork walls of an open hearth furnace, the steps of rapidly batch-mixing 5%10% by weight of water with dry castable refractory material, said refractory material being made from dead burned magnesite having an MgO content of at least about 90% by weight on the basis of an oxide analysis and said castable refractory material being characterized by being quick-setting upon being cast further characterized by a green bonding complex which readily releases free and combined water upon being heated after casting and setting; rapidly substantially continuously conveying immediately after mixing successive batch-mixes of the refractory material to and deposit-placing the same in successive adjacent zones on the furnace sub-hearth brickwork walls; progressively immersion vibrating the refractory material in each zone simultaneously with deposit continuously from zone to zone to compact the thus-cast refractory material; continuing the immersion vibration in each zone for a sufficient time to develop in the deposited and compacted refractory material a density equivalent of 165-175 pounds per cubic foot of compacted refractory material; permitting the placed and compacted material to set; providing form means confining the refractory material as deposited and vibrated and while setting in areas on the sub-hearth brickwork comprising a plurality of adjacent deposit-zones; removing the form means defining any deposit-zone after the refractory material has been com pacted in such deposit-zone; extending the placement and compactment of the refractory material in successive confined areas throughout the furnace bottom fiat and bank walls whereby vibration compactment and setting of the refractory material proceeds progressively and continuously from one zone to another in any confined area as the material is deposited in such area and similarly proceeds progressively and continuously in successive confined areas throughout the furnace bottom flat and bank Walls and eliminates joints in the compacted material throughout the furnace bottom fiat and bank walls; completing the mixing, conveying, depositing and compacting of the thus-cast refractory material of any batch-mix within to minutes; combustion heating the cast bottom material to about 800 F. as rapidly as possible to remove water therefrom While simultaneously discharging from the furnace chamber water vapor resulting from such water removal during such heating; then rapidly combustion heating the cast material to 2900 F. to 2950 F.; and then continuing the combustion heating of the cast material at between 2900 F. and 3000 F. for24 hours to develop ceramic bonds in the refractory material and to complete the formation of a cast, joint-free, monolithic, uniformly and extremely dense, highly refractory entire bottom for the open hearth furnace. V

3. The method set forth in claim 2 in which the water batch-mixed with dry refractory material composition is 8% by weight and is accurately controlled by precisely meter-measuring the quantity of water mixed with each batch of dry refractory material; and in which the rapid batch-mixing is performed thoroughly and uniformly in approximately one minute for each batch-mix.

4. The method of forming from a large mass of 119.5 and more tons of refractory material an entire cast, jointfree, monolithic, uniformly and extremely dense, highly refractory furnace bottom on flat and bank sub-hearth brickwork walls of an open hearth furnace in which successive heats of steel are melted and refined, and of maintaining the thus-formed refractory bottom including the steps of rapidly batch-mixing 5%-10% by weight of water with dry castable refractory material, said refractory material being made from dead burned magnesite having an MgO content of at least about 90% by weight on the basis of an oxide analysis and said castable refractory material being characterized by being quicksetting upon being cast further characterized by a green bonding complex which readily releases free and combined water upon being heated after casting and setting; rapidly substantially continuously immediately after mixing conveying successive batch-mixes of the refractory material to and depositing the same in successive adjacent zones on the furnace sub-hearth brickwork Walls; progressively vibrating the refractory material in each zone simultaneously with deposit continuously from zone to zone to compact and develop high density in the thus-cast refractory material; permitting the placed and compacted material to set; providing form means confining the refractory material as deposited and vibrated and while setting in areas on the sub-hearth brickwork comprising a plurality of adjacent deposit-zones; removing the form means defining any deposit-zone after the refractory material has been compacted in such deposit-zone; extending the placement and compactment of the refractory material in successive confined areas throughout the furnace bottom flat and bank walls whereby vibration comp actment and setting of the refractory material proceeds progressively and continuously from one zone to another in any confined area as the material is deposited in such area and similarly proceeds progressively and continuously in successive confined areas throughout the furnace bottom fiat and bank Walls and eliminates joints in the compacted material throughout the furnace bottom flat and bank walls;completing the mixing, conveying, depositing and compacting of the thus-cast refractory material of any batch-mix within 5 to 15 minutes; combustion heating the cast bottom material to about 800 F. as rapidly as possible to remove water therefrom while simultaneously discharging from the furnace chamber water vapor resulting from such water removal during such heating; then rapidly combustion heating the cast material to 2900 F. to 2950 F; then continuing the combustion heating of the cast material at between 2900 F. and 3000 F. for 24 hours to develop ceramic bonds in the refractory material; and fettling the cast refractory furnace bottom between each heat with sea water magnesite containing at least about 92% MgO by weight.

5. In a method of forming from a large mass of 119.5

and more tons of refractory material an entire cast, jointfree, monolithic, uniform, dense, highly refractory furnace bottom on sub-hearth brickwork walls of an open hearth furnace, the steps of rapidly and continuously mixing casting material, the casting material being comprised of an initimate admixture of size-graded refractory material made from dead burned magnesite and from about 5 to 10%, by weight, based on the weight of the refractory material, of water, at least about by weight, of the refractory material being MgO on the basis of an oxide analysis, said admixture being characterized by rapid self-sustention to a degree sufiicient to bear the weight of a man standing thereon and when cast being characterized by having a green bonding complex capable of readily releasing free and chemically combined water upon being subjected to elevated temperat res; providing form means dividing said sub-hearth brickwork walls into a plurality of contiguous zones; rapidily and substantially continuously conveying the admixture of water and refractory material for deposit in said zones on the furnace sub-hearth brickwork walls; immediately subjecting the deposited material in said zones to vibration for a time period sufiicient to substantially uniformly orient the ingredients of said deposits into a compact and joint-free monolith; removing the form means defining any zone after the refractory material has been compacted in such zone continuing the deposition of the intimate admixture of refractory material and water throughout all the zones on said sub-hearth brickwork walls while continuing said progressive vibration-orientation until said material forms into a joint-free uniform monolith bottom covering the furnace sub-hearth brickwork walls; combustion heating the monolith bottom to a temperature sufficient to cause rapid evolution of free and chemically combined water from the monolith bottion of water vapor evolution rapidly combustion heating during said combustion heating so as to remove evolving water vapor from the furnace; substantially upon termination of Water vapor evolution-rapidly combustion heating the cast material up to a temperature above about 2900 F. and holding said temperature for a time period sufficient for ceramic bonds to develop in the monolith bottom so as to form a joint-free, uniform and dense, highly refractory bottom on the furnace sub-hearth brickwork Walls.

6. The method as set forth in claim 5 in which the mixing, depositing and vibrating of the admixture deposited in any zone is completed in less than about 15 10 minutes.

References Cited by the Examiner Large Cast Sections of Basic Refractories, American Ceramic Society Bulletin, volume 39, pages 456-459, September 1960.

Modern Refractory Practice, 4th Edition, copyright 1961, pages 99, 153, and 166 relied upon.

ROBERT F. WHITE, Primary Examiner.

ALEXANDER H. BRODMERKEL, Examiner.

R. B, MOFFI'IT, Assistant Examiner. 

1. THE METHOD OF FORMING FROM A LARGE MASS OF 119.5 AND MORE TONS OF REFRACTORY MATERIAL AN ENTIRE CAST, JOINTFREE, MONOLITHIC, UNIFORMLY AND EXTREMELY DENSE, HIGHLY REFRACTORY FURNACE BOTTOM ON FLAT AND SLOPPING FRONT, BACK, END AND BANK SUB-HEARTH BRICKWORK WALLS OF AN OPEN HEARTH FURNACE INCLUDING THE STEPS OF APPLYING TREATMENT MATERIAL TO THE SURFACE OF THE SUB-HEARTH BRICKWORK WALLS TO PREBENT THE ABSORPTION OF WATER FROM SUSBEQUENTLY APPLIED CASTABLE MATERIAL; PROVIDING FROM MEANS CONTOURED TO THE PROFILE OF THE SUB-HEARTH FLAT AND SLOPING FRONT, BACK, END AND BANK WALLS DIVIDING THE SUB-HEARTH FLAT INTO CAVITIES EACH EXTENDING FROM THE FRONT TO THE BACK BANK WALL AND INTO CLIMBING CAVITIES EXTENDING ALONG THE SLOPING BANK WALLS; RAPIDLY BATCH-MIXING 5% TO 10% BY WEIGHT OF WATER WITH DRY CASTABLE REFRACTORY MATERIAL, SAID REFRACTORY MATERIAL BEING MADE FROM DEAD BURNED MAGNESITE HAVING AN MGO CONTENT OF AT LEAST ABOUT 90% BY WEIGHT ON THE BASIS OF AN OXIDE ANALYSIS AND SAID CASTABLE REFRACTORY MATERIAL BEING CHARACTERIZED BY BEING QUICK-SETTING UPON BEING CAST FURTHER CHARACTERIZED BY A GREEN BONDING COMPLEX WHICH READILY RELEASES FREE AND COMBINED WATER UPON BEING HEATED AFTER CASTING AND SETTING; RAPIDLY SUBSTANTIALLY CONTINUOUSLY CONVRYING IMMEDIATELY AFTER MIXING SUCCESSIVE BATCH-MIXES OF THE REFRACTORY MATERIAL TO AND DEPOSIT-PLACING THE SAME IN SUCCESSIVE ADJACENT ZONES OF SAID CAVITIES; EXTENDING THE PLACEMENT OF THE MIXED MATERIAL FROM ZONES TO ZONE THROUGHOUT EACH CAVITY AND IN SUCCESSIVE CAVITIES ALONG THE FLAT AND BANK EALLS; PROGRESSIVELY VIBRATING THE REFRACTORY MATERIAL IN EACH ZONE SIMULTANEOUSLY WITH DEPOSIT CONTINUOUSLY FROM ZONE TO ZONE THROUGHOUT ALL SAID CAVITIES TO COMPACT AND DEVELOP HIGH DENSITY IN THE THUS-CAST REFRACTORY MATERIAL AND TO ELIMINATE JOINTS BETWEEN SAID ZONES, MEANWHILE REMOVING THE FORM MEANS DEFINING ANY CAVITY AFTER THE REFRACTORY MATERIAL HAS BEEN COMPACTED IN SUCH CAVITY; COMPLETING THE MIXTURE, CONVEYING, DEPOSIT-PLACING AND COMPACTING OF THE THUS-CAST REFRACTORY MATERIAL OF ANY BATCH-MIX WITHIN 5 TO 15 MINUTES; PERMITTING THE THUS-CAST REFRACTORY MATERIAL TO SET; THEN COMBUSTION HEATING THE CAST BOTTOM MATERIAL TO ABOUT 800*F. AS RAPIDLY AS POSSIBLE TO REMOVE WATER THEREFROM WHILE SIMULTANEOUSLY VENTING AND DISXHARGING FROM THE FURNACE CHAMBER WATER VAPOR RESULTING FROM SUCH WATER REMOVAL DURING SUCH HEATING; THEN RAPIDLY COMBUSTION HEATING THE CAST MATERIAL TO 2900*F. TO 2950*F.; AND THEN CONTINUING THE COMBUSTION HEATING OF THE CAST MATERIAL AT BETWEEN 2900*F. AND 3000*F. FOR 24 HOURS DEVELOP CERAMIC BONDS IN THE REFRACTORY MATERIAL AND TO COMPLETE THE FORMATION OF A CAST, JOINT-FREE, MONOLITHIC, UNIFORMLY AND EXTREMELY DENSE, HIGHLY REFRACTORY ENTIRE BOTTOM FOT THE OPEN HEARTH FURNACE. 